The connection terminals of electrical apparatus, especially electrical apparatus for automotive vehicles, are usually made of copper. A direct connection of these connection terminals and aluminum wires (which includes a conductor core and an insulation layer wrapped over the conductor core, and the conductor core is mainly made of aluminum or aluminum alloy) will result in a large contact resistance. Under a long-term operation, an overloading, or a short circuit of the apparatus, an acute temperature rise can occur on the connection joint, and thus causes accidents. To this end, a pre-treated copper-aluminum connector or a copper-aluminum transition bus bar is generally used in practice.
A Chinese Utility Model Patent CN 203312469 U discloses a copper-aluminum joint, which mainly plays a role of transitional connector between electrical apparatus and aluminum wires. The elements involved in the transitional connector mainly include aluminum wire, aluminum ferrule, and copper terminal. Specifically, the aluminum wire consists of a conductor core and an insulation layer wrapped over the conductor core. The aluminum ferrule is sleeved over the aluminum wires. One end of the aluminum ferrule is placed on the conductor core at the end portion of the aluminum wire where the insulation layer is removed, and the other end of the aluminum ferrule is placed on the adjacent insulation layer. The interior of the aluminum ferrule is of a step shape, and an inner step surface is matched with an end surface of the insulation layer.
However, there is no limitation about the size of the aluminum ferrule for the aluminum-copper joint having such a structure. Since the commonly used aluminum ferrule generally has a yield strength of about 30 MPa, a small wall thickness of the aluminum ferrule when crimped with the aluminum wire will lead to cracks on the aluminum ferrule easily, or obvious cracks may appear after some scratches, thereby degrading the overall mechanical properties of the copper-aluminum joint. While, increasing the wall thickness of the aluminum ferrule contributes very little on improving the crimping performance, mechanical properties, and electrical properties of the product and requires a large amount of aluminum material, which greatly increases the production cost.
Meanwhile, since the aluminum wire is connected to the aluminum ferrule by crimping, if the crimping cannot achieve a good connection, it is easy to leave a gap between the aluminum ferrule and the conductor core of the aluminum wire, or between the conductor cores of the aluminum wire. As a result, it is difficult to isolate air and water, and the conductor core will get oxidized and corroded by air. Thus, the resistance between the conductor core and the aluminum ferrule is increased, and the performance of electrical conductivity between the aluminum wire and the aluminum ferrule is reduced.